Composition containing acrylonitrile polymers and color inhibiting agents therefor and method of making



COMPOSITION CONTAINING 'ACRYLONITRIL POLYMERS AND COLOR INHIBITING AGENTS THEREFOR AND METHOD OF MAKING Richard R. Holmes and Lloyd T. Jenkins, Decatur, Ala., assignors to The Chemstrand Corporation, Decatur, Ala., a corporation of Delaware No Drawing. Filed Aug. 13, 1959, Ser. No. 833,369

14 Claims. (Cl. 260-326) This invention relates to the stabilization of acrylonitrile polymers and blends thereof. More particularly, it relates to the stabilization of acrylonitrile polymers and blends thereof which have a tendency to develop color upon standing or application of heat.

This application is a continuation-in-part of our application Serial No. 586,679, filed May 23, 1956 and now abandoned.

The term polymer, as employed in the instant description and claims, is intended to include homopolymers, copolymers, and blends thereof, said polymers containing at least 80 percent by Weight of polymerized or copolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent ormore of acrylonitrile are generally insoluble in the more common solvents. In those instances where suitable solvents have been found, in order to effect solution, the application of heat is usually necessary. Where heat is employed to effect solutions, from which shaped articles are to be formed, a tan to dark brown color frequently develops in the solutions and therefore is carried over into the product formed therefrom. This color also develops in solutions upon standing for prolonged periods of time.

The mechanism which causes color formation has not been definitely ascertained, although -a variety of reasons therefor have been advanced. The presence of metal ions, such as iron, copper and manganese in the solutions may cause the color. The employment of amide compounds as solvents may result in formation of amina when heat is applied and cause color in the compositions. Impurities present in the solvents have also been cited as a cause. Whatever may be the reason for color formation, it results in compositions and products of undesirable standards and therefore, has been the source of concern, particularly in commercial operations where such types of polymers or copolymers are employed.

Accordingly, it is an object of the present invention to prevent undesirable color formation in acrylonitrile polymer compositions.

Another object is to minimize color formation when solutions of the acrylonitrile polymers are permitted to stand for a prolonged period of time or upon application of heat.

It is also an object of the invention to prevent color formation in acrylonitrile polymers at elevated temperatures.

A still further object of the invention is the production of solutions of acrylonitrile polymers and articles produced therefrom having improved color characteristics.

Other objects and advantages will be apparent from a consideration of the description of the invention which follows hereafter.

In general, the objects of the invention are accomplished by dissolving the polymer of acrylonitrile in a suitable solvent therefor and preventing or minimizing color formation by the presence in the solution as an inhibiting agent, a combined reagent comprising an organic metal sulfoxylate, formaldehyde and an inorganic acid having an ionization constant greater than l 10- ICC 2 Among the sulfoxylates which may be employed in practising the instant invention are those having the genin which R is an alkanol group containing 1 to 3 carbon atoms, an acyl group containing 1 to 3 carbon atoms or an aryl group containing 6 to 8 carbon atoms, n is an integer from 1 to 2, and M is sodium, potassium zinc, etc. Compounds illustrative ofthis class are sodium formaldehyde sulfoxylate, zinc formaldehyde sulfoxylate, potassium formaldehyde sulfoxylate, zinc. acetaldehyde sulfoxylate, sodium acetaldehyde sulfoxylate, potassium acetaldehyde sulfoxylate, zinc propionaldehyde sulfoxylate, sodium propionaldehyde sulfoxylate, potassium propionaldehyde sulfoxylate, etc.

eral formula,

The components of the inhibiting agent may be em-' ployed in equal or unequal amounts,-any one constituent being present in a widely varying amount in a three component system. For example, any one constituent can be present in a range of from 98 to 1 percent in a three component system. It is preferred, however, that each constituent in the inhibiting agent be employed in substantially equal proportions by weight based on the total weight of the inhibiting agent. The total amount of inhibiting agents can be employed in a range of about 0.3 to 15 percent, based on the total polymer Weight. However, it is preferred that the inhibiting agent of the instant invention be present in a small amount compared to the amount of polymer dissolved. ,Thus, although the amount is not critical, it is preferred that the inhibiting agent be present in the amount of about 0.3 to 3.0 percent, based on the total weight of the-polymer. The inhibiting agent may be added to the solvents before or after the polymer is dissolved therein. The inhibiting agent permits exposure to high temperatures for prolonged standing periods Without the development of the objectionable color which usually results in such solutions. The compositions of the instant invention may be prepared in a varying temperature range. For example, the compositions of the instant invention may be prepared by mixing the polymer, a suitable solvent and the inhibiting agent at any temperature or heating the mixture to a temperature up to the boiling point of the solvent.

Among the acids having an ionization constant greater than 1x10"- which may be employed in practicing the instant invention are sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid,- etc.

Among the solvents which may be used in practicing the instant invention are N,N-dimethylformamide, N,N- dimethylacetamide, aqueous zinc chloride, sulfuric acid,

aqueous nitric acid, aqueous sodium thiocyanate, ethylene carbonate, sulfolane, nitromethane, etc.

The polymeric materials, which may be employed in nized as the fiber-forming acrylonitrile polymers, it will be understood that the invention is likewise applicable to polymers containing less than percent acrylonitrile and the same stability is realized with the inhibiting agents defined herein. The acrylonitrile polymers containing less than 80 percent acrylonitrile are useful in forming films, coating compositions, molding operations, lacquers, etc., in all of which applications the alleviation of undesirable color is extremely important.

For example, the polymer many be a copolymer of from 80 to 99 percent acrylonitrile and from 2 to 20 percent of another monomer containing the C=C linkage and copolymerizable with acrylonitrile. Suitable mono-olefinic monomers include acrylic, alpha-chloroacrylic and methacrylic acids; the acrylates, such as methylmethacrylate, ethylmethacrylate, butylmethacrylate, methoxymethyl methacrylate, beta-chloroethyl methacrylate, and the corresponding esters of acrylic and alpha-chloroacrylic acids; vinyl chloride, vinyl fluoride, vinyl bromide, vinylidene chloride, l-chloro-l-bromoethylene; methacrylom'trile; acrylamide and methacrylamide; alpha-chloroacryla'mide, or monoalkyl substitution products thereof; methyl vinyl ketone; vinyl carbo'xylates, such as vinyl acetate, vinyl chloroacetate, vinyl propionate, and vinyl stearate; N-vinylimides, such. as N-vinylphthalimide and N-vinylsuccinimide; methylene malonic esters; itaconic-acid and itaconic ester; N-vinylcarbazole; vinyl furane; alkyl vinyl esters; vinyl sulfonic acid; ethylene alpha, beta-dicarboxylic acids or their anhydrides or derivatives, such as diethylcitraconate, diethylmesaconate, diethylmesaconate, styrene, vinyl naphthalene; vinyl-substituted tertiary heterocyclic amines, such as the vinylpyridines and alkyl-substituted vinylpyrides, for example, 2-vinylpyridine, 4-vinylpyridine, 5- methyl-Z-vinylpyridine, etc.; l-vinylimidazole and alkylsubstituted -1-vinylimidazoles, such as 2-, 4-, or S-methyll-vinylimidazole, and other C=C containing poly- 'merizable materials.

The polymer may be a ternary interpolymer, for example, products obtained by the interpolymerization of crylonitrile and two or more of any of the monomers, other than acrylonitrile, enumerated above. More specifically, and preferably, the ternary polymer comprises acrylonitrile, methacrylonitrile, and 2-vinylpyridine. The ternary'polymers preferably contain from 80 to 97 percent of acrylonitrile, from 1 to percent of a vinyl pyridine or a l-vinylimidazole, and from 1 to 18 percent of another substance, such as methacrylonitrile or vinyl chloride.

The polymer may also be a blend of polyacrylonitrile or of a binary interpolymer of from 80 to 99 percent acrylonitrile and from 1 to 20 percent of at least one other C=C containing substance with from 2 to 50 percent of the weight of the blend of a copolymer of from 10 to 70 percent of arcylonitrile and from 30 to 90 percent of at least one other C=C containing polymerizable monomer. Preferably, when the polymeric material comprises a blend, it will be a blend of a copolymer of 90 to 98 percent acrylonitrile and from 2 to 10 percent of another mono-olefinic monomer, such as vinyl acetate, which is not receptive to dyestuif, with a sufficient amount of a copolymer of from 10 to 70 percent of acrylonitrile and from 30 to 90 percent of a vinyl-substituted tertiary heterocyclic amine, such as vinylpyridine or 1;-vinylimidazole, to give a dyeable blend having an overall vinyl-substituted tertiary heterocyclic amine content of from 2 to 10 percent, based on the Weight of the blend.

The polymers, useful in the practice of the present invention, may be prepared by any conventional polymerization procedures, such as mass polymerization methods, solution polymerization methods, or aqueous emulsion procedures. However, the preferred practice utilizes suspension polymerization wherein the polymer is prepared in finely divided form for immediate use in the fiber fabrication operations. The preferred suspension polymerization may utilize batch procedures, wherein monomers are charged with an aqueous medium containing the necessary catalyst and dispersing agents. A more desirable method involves the semi-continuous ,pro-

4, cedure in which the polymerization reactor containing the aqueous medium is charged with the desired monomers and the continuous withdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any water-soluble peroxy compound, for example the potassium, ammonium and other water-soluble salts of peroxy acids, sodium peroxide, hydrogen peroxide, sodium perborate, the sodium salts of other peroxy acids, and any other water-soluble compound containing a peroxy group (OO). A wide variation in the quantity of peroxy compound is possible. For example, from 0.1 to 3.0 percent by weight of the polymerizable monomer may be used. The catalyst may be charged at the outset of the reaction, or it may be added continuously or in increments throughout the reaction for the purpose of maintaining a more uniform concentration of catalyst in the reaction mass. The latter method is preferred because it tends to make the resultant polymer more uniform in its chemical and physical properties.

Although the uniform distribution of the reactants throughout the reaction mass can be achieved by vigorous agitation, it is generally desirable to promote the uniform distribution of reagents by using inert wetting agents, or emulsion stabilizers. Suitable reagents for this purpose are the water-soluble salts of fatty acids, such as sodium oleate and potassium stearate, mixtures of water-soluble fatty acid salts, such as common soaps prepared by the saponification of animal and vegetable oils, the amino soaps, such as salts of triethanolamine and dodecylmethylamine, salts of rosin acids and mixtures thereof, the water-soluble salts of half esters of sulfuric acid and long chain aliphatic alcohols, sulfonated hydrocarbons, such as alkyl aryl sulfonates, and any other of a wide variety of wetting agents, which are in general organic compounds containing both hydrophobic and hydrophilic radicals. The quantity of emulsifying agents will depend upon the particular agents selected, the ratio of monomer to be used, and the conditions of polymerization. In general, however, from 0.01 to 1.0 percent by Weight of the monomers may be employed.

The emulsion polymerizations are prferably conducted in glass or glass-lined vessels which are provided with a means for agitating the contents. Generally rotary stirring devices are the most effective means of insuring the intimate contact of the reagents, but other methods may be successfully employed, for example by rocking or tumbling the reactors. The polymerization equipment-generally used is conventional in the art and the adaptation of a particular type of apparatus to the reaction contemplated is within the province of one skilled in the art. The articles manufactured therefrom may be produced by well-known conventional methods, for example, the wet-spinning, dry-spinning and meltspinning methods for producing fibers.

The following examples are illustrative rather than limitative and all parts, proportions and percentages are by weight unless otherwise specified. The tests for color indicative of approaching whiteness used throughout the examples consist of measurements of brightness and purityas calculated from the tristimulus values determined on a General Electric Spectrophotometer in accordance with the methods recommended by the Standard Observer and Coordinate System'of the International Commission on Illumination, as fully set forth in the Handbook of Calorimetry published by the Technology Press, Massachusetts Institute of Technology 1935. The test results are given in figures which indicate a greater whiteness or purity as they decrease towards zero.

EXAMPLE I percent of acrylonitrile and 50 percent of 2-methyl 5- purity is set forth below.

Table I Inhibitor Percentage Purity Used 1 Control- 7. Sodium Formaldehyde sulfoxylate, Formaldehyde and Sulfuric Aicd 3 2. 1

1 Percentage used is the total amount of inhibiting agent based on the total Weight of the polymer.

EXAMPLE 11 7.5 grams of a copolymer containing 94 percent of acrylonitrile and 6 percent of vinyl acetate were added to 45 milliliters of N,N-dimethylacetarnide containing approximately 0.05 grams of titanium dioxide. The mixture was stirred and heated for 35 minutes at 70 C. -It was then quickly cooled to room temperature and the color measured. This sample was used as a control. The purity is set forth below. Subsequently, a like sample was prepared but with 0.225 gram of an inhibiting agent containing 0.075 grams each of sodium formaldehyde sulfoxylate, formaldehyde and sulfuric acid. The purity is set forth below.

Table II Inhibitor Percentage Purity Used 1 Control. 10. 2 Sodium Formaldehyde sulfoxylate, Formaldehyde and Sulfuric Acid 3 3.2

1 Percentage used is the total amount of inhibiting agent based on the total weight of the polymer.

EXAMPLE III Table III Inhibitor Percentage Purity Used 1 Control. 8. 5 Sodium Formaldehyde Sulioxylate, Formaldehyde and Sulfuric Acid 3 2. 2

1 Percentage used is the total amount of inhibiting agent based on the total weight of the polymer.

EXAMPLE IV 7.5 grams of a polymer blend of a copolymer containing 94 percent of acrylonitrile and 6 percent of vinyl acetate and 12 percent of a copolymer of 50 percent of acrylonitrile and 50 percent of Z-methyl-S-vinylpyridine were added to 45 milliliters of N,N-dimethylacetamide containing approximately 0.05'grarn of titanium dioxide. The mixture was stirred and heated for 35 minutes at 70 C.

The mixture was stirred and heated 6 It was then quickly cooled to room temperature and the color measured. This sample was used as a control and the purity is set forth below. Subsequently, like samples were prepared containing 0.225 gram, as a color inhibitor, of a compound selected from sodium formaldehyde sulfoxylate, formaldehyde and sulfuric acid; 0.1125 gram each of formaldehyde and sulfuric acid as a combined color inhibiting agent; 0.1125 gram each of sodium formaldehyde sulfoxylate and formaldehyde as a combined color inhibiting agent; and finally a sample was prepared containing 0.075 gram each of sodium formaldehyde sulfoxylate, formaldehyde and sulfuric acid. The purity of these samples are set forth in the following table.

Table IV Inhibitor Percentage Purity Used 1 Control 3. 0 7. 0 Sodium Formaldehyde Sulfoxylate 3.0 4. l Formaldehyde 3. 0 5. 5 Sulfuric Acid 3. O 5. 6 Sodium Formaldehyde Sulfoxylate and Formaldehyde 3. O 3. 6 Sodium Formaldehyde sulfoxylate and S lfuric Acid 3. 0 4. 2 Formaldehyde and Sulfuric Acid. 3.0 4.6 Sodium Formaldehyde sulfoxylate, Formaldehyde and Sulfuric Acid 3.0 2.1

1 Percentage used is the total amount of inhibiting agent based on the total weight of the polymer.

The data in the above table show that where a combined color inhibiting agent containing sodium formaldehyde sulfoxylate, formaldehyde and sulfuric acid is employed, it produces a purity reading lower than an inhibiting agent containing only sodium formaldehyde sulfoxylate, formaldehyde or sulfuric acid alone, or a combined inhibiting agent containing two components such as sodium formaldehyde sulfoxylate and formaldehyde, sodium formaldehyde sulfoxylate and sulfuric acid or formaldehyde and sulfuric acid.

The compositions of the instant invention present many advantages. For example, products formed from the polymer solutions of the instant invention are free of objectionable color and therefore of greater commercial value. In preparing the polymer solutions, heat may be applied without the danger of color formation and the solutions, if necessary, may stand for prolonged periods and remain free of color. The inhibiting agents are readily available and inexpensive. Therefore, no great increase in production cost is necessary. The compositions containing the inhibitors may be prepared without going through detailed and elaborate procedures that necessitate expensive changes in the design of the apparatus used to manufacture them.

i It -will be understood to those skilled in the art that many apparently widely different embodiments of this invention can be made'without departing from the spirit and scope thereof. Accordingly, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. A new composition of matter comprising a polymer selected from the group consisting of polyacrylonitrile and a copolymer containing at least percent of polymerized acrylonitrile with up to 20 percent of another mono-olefinic monomer, copolymerized therewith, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of a color inhibiting agent, said color inhibiting agent containing equal proportions by weight of a compound having the general formula,

wherein R is an alkanol group containing 1 to 3 carbon atoms and having the free valence on a carbon atom joined directly to the hydroxy group, n is an integer from 1 to 2 and M is a metal selected from the group consisting of sodium, potassium and zinc; formaldehyde and an inorganic acid having an ionization constant greater than 1X 10- '2. A new composition of matter as defined in claim 1 wherein the polymer is a copolymer containing from 80 to 98 percent of acrylonitrile and from 2 to 20 percent of another polymerizable mono-olefinic monomer copolymerized therewith. 3. A new composition of matter as defined in claim 1 wherein the polymer is a blend of 80 to 99 percent of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate copolymerized therewith, and 1 to 20 percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of 2-methy1-5-vinyl pyridine copolymerized therewith. t

4. A new composition of matter as defined in claim 1 wherein the polymer is polyacryloni-trile.

5. A new composition of matter as defined in claim 1 wherein the compound is sodium formaldehyde sulfoxylate.

6. A new composition of matter as defined in claim 1 wherein the compound is potassium formaldehyde sulfoxylate.

7. A new composition of matter as defined in claim 1 wherein the compound is zinc formaldehyde sulfoxylate.

8. A new composition of matter as defined in claim 1 wherein the solvent is N,N-dimethylacetamide. 9. A new composition of matter comprising a polymer blend of (A) a copolymer containing 90 to 98 percent'of acrylonitrileand 2 to lpercent of another polymerizable mono-olefinic monomer copolymerized therewith, and (B) a copolymer containing to 70 percent of acrylonitrile and 30 to 90 percent of a vinyl-substituted tertiary heterocyclic amine copolymerized therewith, said blend having an overall vinyl-substituted tertiary heterocyclic amine content of from 2 to 10 percent base on the weight of the blend, a solvent therefor, and 0.3 to percent based on the total weight of the polymer, of a color inhibiting agent containing equal proportions by weight of a compound having the general formula,

matter comprising mixing a polymer containing at least 80 percent of polymerized acrylonitrile and up to 20 percent of another polymerizable mono-olefinic monomer copolymerized therewith, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of a color inhibiting agent containing equal proportions of a compound having the general formula,

wherein R is an alkanol group containing 1 to 3 carbon atoms, and having the free valence on a carbon atom joined directly to the hydroxy group, n is an integer from 1 to 2 and M is a metal selected from the group consisting of sodium, potassium and zinc; formaldehyde and an inorganic acid having an ionization constant greater than 1 10- and heating the mixture to form a homogeneous solution.

11. The'method as defined in claim 10 wherein the polymer is a copolymer containing from 80 to 98 percentof acrylonitrile and from 2 to 20 percent of another polymerizable mono-olefinic monomer copolymerized therewith.

12. The method as defined in claim 10 wherein the polymer is a blend of 80 to 99 percent of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate copolymerized therewith, and 1 to 20 percent of (B) a copolymer containing 10 to percent of acrylonitrile and 30 to 90 percent of '2-methyl-5-vinyl pyridine copolymerized therewith.

13. The method as defined in claim 10 wherein the polymer is polyacrylonitrile.

14. A method for preparing a new composition of matter comprising mixing a polymer blend of to 99 percent of (A) a copolymer containing M98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate copolymerized therewith and 1 to 20 percent of (B) a coploymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of Z-methyl-S-vinyl pyridine copolymerized therewith,'a solvent therefor, and 3 percent, based onthe total weight of the polymer, of a color inhibiting agent, said color inhibiting agent containing equal proportions by weight of sodium formaldehyde sulfoxylate, formaldehyde and sulfuric acid, and heating the mixture to a temperature in a range of 25 C. to the boiling point of said mixture to form a homogeneous solution.

References Cited in the file of this patent UNITED STATES PATENTS 2,502,030 Scheiderbauer Mar. 28, 1950 FOREIGN PATENTS 1,027,445 France Feb. 18, 1953 

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER SELECTED FROM THE GROUP CONSISTING OF POLYACRYLONITRILE AND A COPOLYMER CONTAINING AT LEAST 80 PERCENT OF POLYMERIZED ACRYLONITRILE WITH UP TO 20 PERCENT OF ANOTHER MONO-OLEFINIC MONOMER, COPOLYMERIZED THEREWITH, A SOLVENT THEREFOR, AND 0.3 TO 15 PERCENT, BASED ON THE TOTAL WEIGHT OF THE POLYMER, OF A COLOR INHIBITING AGENT, SAID COLOR INHIBITING AGENT CONTAINING EQUAL PROPORTIONS BY WEIGHT OF A COMPOUND HAVING THE GENERAL FORMULA, 